Notwithstanding the fact that none of the planets known to us have a solid atmosphere like our earth and I don’t think any star, I have no explanation why they are all almost round, what phenomenon is behind this (erosion does not seem to me to be valid explanation)?
Answer
Our friend Newton has the answer: gravity. Matter attracts matter. Everything is contracted into a sphere under their own weight and gravity. That is why one of the definitions of a planet is: it must be round or heavy enough to pull itself into a sphere. Actually an ellipsoid (the equator is somewhat thicker due to the centrifugal force). Stars and gas giants are even easier to round: that is plasma or gas and that is easily drawn into a sphere.
Answered by
dr. Jan Buytaert
Biomedical Physics and Optics: *middle and inner ear mechanics *electro-optics *tomography *interferometry *3D imaging *endoscopy *image processing *profilometry *topography *programming *classical physics
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